The demand for high pressure oxygen gas is increasing due to the greater use of high pressure oxygen in partial oxidation processes such as coal gasification for power generation, hydrogen production, and steelmaking. Often nitrogen is also employed in these processes.
Oxygen gas is produced commercially in large quantities generally by the cryogenic rectification of air. One way of producing the oxygen gas at high pressure is to compress the product oxygen gas from the cryogenic rectification plant. This, however, is costly both in terms of the capital costs for the product oxygen compressor and also in terms of the operating costs to power the product oxygen compressor. Another way of producing high pressure oxygen gas is to operate the cryogenic rectification plant at a higher pressure thus producing the oxygen at a higher initial pressure and reducing or eliminating downstream compression requirements. Unfortunately, operating the cryogenic rectification plant at a higher pressure reduces the efficiency of the production process because component separation depends on the relative volatilities of the components which decrease with increasing pressure. This is particularly the case when high pressure nitrogen product is also desired from the cryogenic rectification plant because the removal of nitrogen from the high pressure distillation column as product reduces the amount of reflux which may be employed thus reducing oxygen recovery.
Accordingly, it is an object of this invention to provide a cryogenic rectification system which can produce high pressure product gas with improved efficiency over results attainable with conventional systems, particularly if both oxygen and high pressure nitrogen product gas is desired.